Transistors are key components of modern integrated circuits. To satisfy the requirements of increasingly faster speed, the drive currents of transistors need to be increasingly greater. Since the drive currents of transistors are proportional to gate widths of the transistors, transistors with greater widths are preferred. The increase in gate widths, however, conflicts with the requirements of reducing the sizes of semiconductor devices. Fin field-effect transistors (FinFET) were thus developed.
In state-of-the-art circuits, the operational frequency of the integrated circuit is in the order of several hundreds of mega-hertz (MHz) to several giga-hertz (GHz). In such circuits, the rising time of clock signals is very short, so that voltage fluctuations in the supply line can be very large. Undesired voltage fluctuations in the power supply line powering a circuit can cause noise on its internal signals and degrade noise margins. The degradation of noise margins can reduce circuit reliability or even cause circuit malfunction.
To reduce the magnitude of voltage fluctuations in the power supply lines, filtering, or decoupling capacitors may be used. Decoupling capacitors act as charge reservoirs that additionally supply currents to circuits when required to prevent momentary drops in supply voltage.
In an attempt to incorporate the decoupling capacitor with the other circuitry, the decoupling capacitor has been placed on-chip. One attempt at using an on-chip decoupling capacitor utilizes a thin-film planar capacitor. These capacitors, however, generally require large areas and are difficult to design and fabricate such that the capacitors have a sufficiently large enough capacitance.